This disclosure relates generally to oil or gas producing wells, and, more specifically, the disclosure is directed to horizontal wells having a gas vent system for removing gas from a wellbore.
The use of directionally drilled wells to recover hydrocarbons from subterranean formations has increased significantly in the past decade. A large number of wells exist whereby a substantially vertical section is drilled to a depth where hydrocarbon source rock has been identified, and then the direction of the well is turned to follow the path of the source rock along a substantially horizontal distance. The geometry of the wellbore along the substantially horizontal portion typically exhibits elevation changes, such that one or more peaks and valleys occur. It is typical for multiple production zones to be provided along the length of the substantially horizontal section of the wellbore, such that materials can pass from the formation into the wellbore, then be channeled along the wellbore. These materials may consist of one or more of gaseous, liquid, or solid phase substances.
In at least some known horizontal wells, the transport of both liquid and gas phase materials along the wellbore results in unsteady flow regimes including slugging, or gas slugging. Under the influence of gravity, the liquid and solid phase materials having higher density tend to settle in the lower elevation valleys of the wellbore, while the lower density gas phase materials tend to collect in the higher elevation peaks of the wellbore. Fluids that have filled the wellbore in lower elevations impede the transport of gas along the length of the wellbore. This phenomena results in a buildup of pressure along the length of the substantially horizontal wellbore section, reducing the maximum rate at which fluids can enter the wellbore from the formation. Continued inflow of fluids and gasses cause gas the trapped gas pockets to build in pressure and in volume until a critical pressure and volume is reached, whereby a portion of the trapped gas escapes passed the fluid blockage and migrates as a slug along the wellbore.
Furthermore, at least some known horizontal wells include pumps that are designed to process pure liquid or a consistent mixture of liquid and gas. However, under slugging conditions, when the pump encounters a slug of gas, the pump is operating in dry conditions for a period of time until the gas slug passes and liquid again reaches the pump. Operating the pump without liquids may cause a reduction in the expected operational lifetime of the pump. Additionally, the pump may undergo a large load fluctuation during slugging conditions. More specifically, the pump requires a relatively large amount of power to lift large volumes of liquid during standard operation. When a gas slug reaches the pump, the pump may experience a drop in power consumption because it is no longer doing work. Subsequently, when liquid encounters the pump again, the power consumption increases significantly over a relatively short period of time. Such load fluctuations reduce pumping efficiency and may further reduce the expected operational lifetime of the pump, the driver that operates the pump, and the power delivery system that supplies power to the pump.